Generally, the commercially available photo printer can transfer images to film papers in order to print out colorful photos. In recent years, small-sized photo printers have been introduced into the market. The small-sized photo printer has the advantage of small volume. Moreover, the small-sized photo printer can receive images from smart phones or other electronic devices in a wireless transmission manner and thus print out the photos. Consequently, the photo printers are favored by users.
For example, the structure of a conventional photo printer is disclosed in U.S. Pat. No. 7,371,025. The conventional photo printer comprises a film paper tray, an image reading and writing region, plural transfer rollers and plural distribution rollers. The image reading and writing region comprises a light source module. The operations of the conventional photo printer will be simply described as follows. After the conventional photo printer is enabled, the film paper placed on the film paper tray is transferred to the image reading and writing region. The light source module of the image reading and writing region emits light beams. The light beams are projected onto the film paper. Consequently, the exposure of the film paper is performed. Then, the film paper is transferred to the region between the plural distribution rollers. Since the film paper is pressed by the plural distribution rollers, the developer liquid in the film paper flows out and the film paper is developed. Afterwards, the developed film paper is outputted.
FIG. 1 schematically illustrates the relationship between a light source module and a film paper of a conventional photo printer. The light source module 1 of the conventional photo printer comprises plural first light sources 11, plural second light sources 12, plural third light sources 13 and a rod lens array 14. The first light sources 11 emit red light beams. The second light sources 12 emit green light beams. The third light sources 13 emit blue light beams. The rod lens array 14 is arranged between the plural first light sources 11, the plural second light sources 12, the plural third light sources 13 and a film paper 10. After the light beams with various colors are transmitted through the rod lens array 14, the light beams are projected onto the film paper 10.
The inner structure and the exposure operation of the film paper will be descried as follows. Please refer to FIG. 1 and FIG. 2. FIG. 2 schematically illustrates a portion of the conventional film paper during the exposure operation. The film paper 10 comprises a surface layer 101, a red photosensitive gel layer 102, a green photosensitive gel layer 103, a blue photosensitive gel layer 104, an image receiving layer 105 and a gap 106.
During the exposure operation of the film paper 10, the light source module 1 is enabled to emit the light beams. That is, the first light sources 11 emit the red light beams B1, the second light sources 12 emit the green light beams B2, and the third light sources 13 emit the blue light beams B3. After the red light beams B1 are transmitted through the rod lens array 14, the red light beams B1 are projected to the film paper 10. After the red light beams B1 are transmitted through the surface layer 101, the red light beams B1 are projected to the red photosensitive gel layer 102. Consequently, the cyan dye molecules that are disposed in the red photosensitive gel layer 102 and projected by the red light beams B1 are fixed in the red photosensitive gel layer 102.
Similarly, after the green light beams B2 are transmitted through the rod lens array 14 and the surface layer 101, the green light beams B2 are projected to the green photosensitive gel layer 103. Consequently, the magenta dye molecules that are disposed in the green photosensitive gel layer 103 and projected by the green light beams B2 are fixed in the green photosensitive gel layer 103.
Similarly, after the blue light beams B3 are transmitted through the rod lens array 14 and the surface layer 101, the blue light beams B3 are projected to the blue photosensitive gel layer 104. Consequently, the yellow dye molecules that are disposed in the blue photosensitive gel layer 104 and projected by the blue light beams B3 are fixed in the blue photosensitive gel layer 104.
Moreover, white light beams are projected to the red photosensitive gel layer 102, the green photosensitive gel layer 103 and the blue photosensitive gel layer 104. Consequently, the dye molecules that are disposed in the photosensitive gel layers 102, 103 and 104 and projected by the white light beams are fixed in the photosensitive gel layers 102, 103 and 104.
The developing operation of the film paper will be descried as follows. Please refer to FIG. 1 and FIG. 3. FIG. 3 schematically illustrates a portion of the conventional film paper during the developing operation. During the developing operation of the film paper 10, the film paper 10 is pressed and squeezed. Consequently, a developer pool (not shown) of the film paper 10 is broken and a developer liquid 107 in the developer pool flows to the red photosensitive gel layer 102, the green photosensitive gel layer 103, the blue photosensitive gel layer 104 and the image receiving layer 105 through the gap 106. During the developing operation, the fixed dye molecules in the photosensitive gel layers 102, 103 and 104 are not influenced by the developer liquid 107. Except for the fixed dye molecules, the other dye molecules in the photosensitive gel layers 102, 103 and 104 are delivered to the image receiving layer 105 by the developer liquid 107. Consequently, the film paper 10 is developed, and the image is shown on the film paper 10.
Generally, the first light sources 11, the second light sources 12 and the third light sources 13 in the light source module 1 of the conventional photo printer are provided by a liquid crystal display (LCD) or an organic light emitting diode (OLED). Since the luminous efficiency of LCD and OLED is not high, the time period of performing the exposure operation of the film paper 10 is long. For showing the white part of the image, the light source module 1 of the conventional photo printer has to project white light beams to the corresponding area of the film paper 10. Since the white light beam is a mixture of the red, green and blue light beams, the method of exposing the white part of the image by the light source module 1 is complicated. Firstly, the first light sources 11, the second light sources 12 and the third light sources 13 emit the red light beams, the green light beams and the blue light beams. Then, the red light beams, the green light beams and the blue light beams are projected to the corresponding area of the film paper 10. Consequently, the exposure operation on the corresponding colors is performed. That is, for exposing the white part of the image, the corresponding area of the film paper 10 needs to be exposed by the red, green and blue light beams. Since the exposure time is long, it is difficult to increase the printing speed of the conventional photo printer.
Therefore, there is a need of providing an improved light source module of a photo printer in order to shorten the exposure time.